[libc++][spaceship] P1614R2: Removed ops from `unordered_multiset`, `unordered_set`

[H-G-Hristov]

Summary

Implements parts of P1614R2:

• Removed ops from unordered_multiset,
• Removed ops from unordered_set

[H-G-Hristov]

Updated table

[H-G-Hristov]

Rebased

[Mordante]

LGTM!

libcxx/docs/Status/SpaceshipProjects.csv

 | `[array.overview] <https://wg21.link/array.overview>`_ (`general <https://wg21.link/container.opt.reqmts>`_),| removed by `issue LWG3347 <https://cplusplus.github.io/LWG/issue3347>`_,None,"| Adrian Vogelsgesang
 | Hristo Hristov",|Complete|
 | `[associative.map.syn] <https://wg21.link/associative.map.syn>`_ (`general <https://wg21.link/container.opt.reqmts>`_),"| `map <https://reviews.llvm.org/D145976>`_
 | `multimap <https://reviews.llvm.org/D145976>`_",[expos.only.func],Hristo Hristov,|Complete|
 | `[associative.set.syn] <https://wg21.link/associative.set.syn>`_ (`general <https://wg21.link/container.opt.reqmts>`_),"| `multiset <https://reviews.llvm.org/D148416>`_
 | `set <https://reviews.llvm.org/D148416>`_",[expos.only.func],Hristo Hristov,|Complete|
 | `[unord.map.syn] <https://wg21.link/unord.map.syn>`_,"| remove ops `unordered_map`
 | remove ops `unordered_multimap`",None,Unassigned,|Not Started|
-| `[unordered.set.syn] <https://wg21.link/unordered.set.syn>`_,"| remove ops `unordered_set`
-| remove ops `unordered_multiset`",None,Unassigned,|Not Started|
+| `[unordered.set.syn] <https://wg21.link/unordered.set.syn>`_,"| remove ops `unordered_set <https://reviews.llvm.org/D152643>`_
+| remove ops `unordered_multiset <https://reviews.llvm.org/D152643>`_",None,Hristo Hristov,|Complete|
 | `[queue.syn] <https://wg21.link/queue.syn>`_,| `queue <https://reviews.llvm.org/D146066>`_,None,Hristo Hristov,|Complete|
 | `[stack.syn] <https://wg21.link/stack.syn>`_,| `stack <https://reviews.llvm.org/D146094>`_,None,Hristo Hristov,|Complete|
 | `[queue.ops] <https://wg21.link/queue.ops>`_,| `queue <https://reviews.llvm.org/D146066>`_,None,Hristo Hristov,|Complete|
 | `[stack.ops] <https://wg21.link/stack.ops>`_,| `stack <https://reviews.llvm.org/D146094>`_,None,Hristo Hristov,|Complete|
 - `5.8 Clause 23: Iterators library <https://wg21.link/p1614r2#clause-23-iterators-library>`_,,,,
 | `[iterator.synopsis] <https://wg21.link/iterator.synopsis>`_,|,None,Unassigned,|Not Started|
 | `[reverse.iter.cmp] <https://wg21.link/reverse.iter.cmp>`_,| `reverse_iterator <https://reviews.llvm.org/D113695>`_,None,Mikhail Maltsev,|Complete|
 "| `[move.iterator] <https://wg21.link/move.iterator>`_

libcxx/include/unordered_set

 template <class Value, class Hash, class Pred, class Alloc>
     bool
     operator==(const unordered_set<Value, Hash, Pred, Alloc>& x,
                const unordered_set<Value, Hash, Pred, Alloc>& y);
 
 template <class Value, class Hash, class Pred, class Alloc>
     bool
     operator!=(const unordered_set<Value, Hash, Pred, Alloc>& x,
-               const unordered_set<Value, Hash, Pred, Alloc>& y);
+               const unordered_set<Value, Hash, Pred, Alloc>& y); // removed in C++20
 
 template <class Value, class Hash = hash<Value>, class Pred = equal_to<Value>,
           class Alloc = allocator<Value>>
 class unordered_multiset
 {
 public:
     // types
     typedef Value                                                      key_type;

 template <class Value, class Hash, class Pred, class Alloc>
     bool
     operator==(const unordered_multiset<Value, Hash, Pred, Alloc>& x,
                const unordered_multiset<Value, Hash, Pred, Alloc>& y);
 
 template <class Value, class Hash, class Pred, class Alloc>
     bool
     operator!=(const unordered_multiset<Value, Hash, Pred, Alloc>& x,
-               const unordered_multiset<Value, Hash, Pred, Alloc>& y);
+               const unordered_multiset<Value, Hash, Pred, Alloc>& y); // removed in C++20
 }  // std
 
 */
 
 #include <__algorithm/is_permutation.h>
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
 #include <__debug>
operator==(const unordered_set<_Value, _Hash, _Pred, _Alloc>& __x,
     {
         const_iterator __j = __y.find(*__i);
         if (__j == __ey || !(*__i == *__j))
             return false;
     }
     return true;
 }
 
+#if _LIBCPP_STD_VER <= 17
+
 template <class _Value, class _Hash, class _Pred, class _Alloc>
 inline _LIBCPP_INLINE_VISIBILITY
 bool
 operator!=(const unordered_set<_Value, _Hash, _Pred, _Alloc>& __x,
            const unordered_set<_Value, _Hash, _Pred, _Alloc>& __y)
 {
     return !(__x == __y);
 }
 
+#endif
+
 template <class _Value, class _Hash = hash<_Value>, class _Pred = equal_to<_Value>,
           class _Alloc = allocator<_Value> >
 class _LIBCPP_TEMPLATE_VIS unordered_multiset
 {
 public:
     // types
     typedef _Value                                                     key_type;
     typedef key_type                                                   value_type;
for (const_iterator __i = __x.begin(), __ex = __x.end(); __i != __ex;)
             _VSTD::distance(__yeq.first, __yeq.second) ||
                   !_VSTD::is_permutation(__xeq.first, __xeq.second, __yeq.first))
             return false;
         __i = __xeq.second;
     }
     return true;
 }
 
+#if _LIBCPP_STD_VER <= 17
+
 template <class _Value, class _Hash, class _Pred, class _Alloc>
 inline _LIBCPP_INLINE_VISIBILITY
 bool
 operator!=(const unordered_multiset<_Value, _Hash, _Pred, _Alloc>& __x,
            const unordered_multiset<_Value, _Hash, _Pred, _Alloc>& __y)
 {
     return !(__x == __y);
 }
 
+#endif
+
 _LIBCPP_END_NAMESPACE_STD
 
 #if _LIBCPP_STD_VER >= 17
 _LIBCPP_BEGIN_NAMESPACE_STD
 namespace pmr {
 template <class _KeyT, class _HashT = std::hash<_KeyT>, class _PredT = std::equal_to<_KeyT>>
 using unordered_set = std::unordered_set<_KeyT, _HashT, _PredT, polymorphic_allocator<_KeyT>>;